THE TONGUE. 7 



the layers of smallest cells, for although no new development of 

 cells can here be directly observed, yet the analogy with other 

 epidermic structures, and the frequent occurrence of two nuclei 

 in the cells of these layers, nay, even of constricted cells 

 (Bowman, compare § 46), are striking facts in favour of the 

 multiplication of the cells which already exist (by division) and 

 against their actual new formation. 



The epithelium of the oral cavity, although thick, is yet readily 

 permeable, differing widely in this respect from the epidermis, 

 which presents similar relations, only in the stratum Malpighii. 

 Fluids of the most different description permeate it from with- 

 out, and once in contact with the mucous membrane, may 

 either be absorbed by its vessels, or perceived by its nerves. 

 Other conditions remaining the same, the activity of the sensi- 

 tive and absorbent powers will depend upon the thinness of the 

 epithelial layer, particularly of the plates, which must always 

 be least permeable, and upon the abundance and superficiality 

 of the vessels and nerves; and these considerations readily 

 explain why the lips, in which the papillae are very numerous, 

 and nearly reach the surface of the epidermis, possess a more 

 delicate sensibility than the gums ; and why the point of the 

 tongue, whose papillae even project with a thinner covering, is 

 still more sensitive (compare, also, on the import of the axile 

 Corpuscles, § 39). The epithelium is permeable outwards, as 

 well as inwards, and permits of the passage of plasma from the 

 vessels of the mucous membrane into the cavity of the mouth. 

 In this manner, like the epidermis in relation to the cutaneous 

 perspiration, it participates in the formation of the mucous 

 fluid, which is yielded, not only by the glands which open into 

 the oral cavity, but also by the whole surface of the mucous 

 membrane. ] 



B. OP THE TONGUE. 



15 131. 

 The Tongue is a mass of muscles attached to a particular 

 bone, the os hyoides, and covered by the mucous membrane of 

 the cavity of the mouth; its muscular elements, 0*009 — 0023'" 

 in breadth, are distinguished from those of the external trans- 

 versely striated muscles, only by being interwoven in the most 



